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S V A S M 0 2 A two-pass cross-referencing assembler for 6502 and 65C02 microproccessors Written by John Michne, KM2H 10 Evergreen Ave. Clifton Park, New York 12065 Version 1.0 May, 1988 S V A S M 0 2 USER'S MANUAL - Version 1.0 - May, 1988 TABLE OF CONTENTS INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . 1 RUNNING THE SVASM02 ASSEMBLER. . . . . . . . . . . . . . 1 Source filename. . . . . . . . . . . . . . . . . . . . 1 Object filename. . . . . . . . . . . . . . . . . . . . 1 Print filename . . . . . . . . . . . . . . . . . . . . 2 INPUT FILE LINE STRUCTURE. . . . . . . . . . . . . . . . 2 Label field. . . . . . . . . . . . . . . . . . . . . . 2 Instruction field. . . . . . . . . . . . . . . . . . . 2 Argument field . . . . . . . . . . . . . . . . . . . . 3 Comment field. . . . . . . . . . . . . . . . . . . . . 3 ARITHMETIC . . . . . . . . . . . . . . . . . . . . . . . 3 Symbols. . . . . . . . . . . . . . . . . . . . . . . . 3 Program counter. . . . . . . . . . . . . . . . . . . . 3 Constants. . . . . . . . . . . . . . . . . . . . . . . 3 Expressions. . . . . . . . . . . . . . . . . . . . . . 4 Arithmetic operators . . . . . . . . . . . . . . . . . 4 Logical operators. . . . . . . . . . . . . . . . . . . 5 ADDRESSING MODE SYNTAX . . . . . . . . . . . . . . . . . 5 6502 Addressing modes. . . . . . . . . . . . . . . . . 5 65C02 Additional addressing modes. . . . . . . . . . . 7 ASSEMBLER DIRECTIVES (Psuedo-ops). . . . . . . . . . . . 8 .BYTE. . . . . . . . . . . . . . . . . . . . . . . . . 8 .WORD. . . . . . . . . . . . . . . . . . . . . . . . . 8 .CMOS. . . . . . . . . . . . . . . . . . . . . . . . . 9 .END . . . . . . . . . . . . . . . . . . . . . . . . . 9 .LIST. . . . . . . . . . . . . . . . . . . . . . . . . 9 .NOLIST. . . . . . . . . . . . . . . . . . . . . . . . 9 .INCLUDE . . . . . . . . . . . . . . . . . . . . . . . 9 .PAGE. . . . . . . . . . . . . . . . . . . . . . . . . 9 .WIDTH . . . . . . . . . . . . . . . . . . . . . . . .10 .PRINTC. . . . . . . . . . . . . . . . . . . . . . . .10 .IF, .ELSE, .ENDIF, .LISTF . . . . . . . . . . . . . .10 ERRORS . . . . . . . . . . . . . . . . . . . . . . . . .11 Fatal errors . . . . . . . . . . . . . . . . . . . . .11 Invocation errors. . . . . . . . . . . . . . . . . . .11 Assembler errors . . . . . . . . . . . . . . . . . . .12 APPENDIX A SVASM02 LST Output File Description. . . . . . . . . .14 APPENDIX B SVASM02 HEX Object File Description. . . . . . . . . .16 COPYRIGHT NOTICE The SVASM02 program and User's Manual are Copyright 1988 by John Michne. Both may be freely copied and distributed for PRIVATE, NON-PROFIT, NON-COMMERCIAL USE ONLY. The SVASM02 program and User's Manual may not be copied and distributed commercially except as arranged with the author. The author makes no warranty or guarantee of suitability of SVASM02 for any purpose, and will not be held liable for any damages, direct or consequential, that may arise due to the use of this software. INTRODUCTION SVASM02 is a two-pass cross-referencing assembler for 6502 and 65C02 microprocessors. It runs in IBM and compatible machines, and has been run under both PC-DOS (Version 3.1) and MSDOS (Version 2.11). Since it is written in 8086 assembly language, memory requirerments are minimal and execution speed is optimum. It is approximately 12K long, and will run in as little as 64K. The original Version 1.0 distribution was via GEnie to the public domain. This was primarily to get the program out to where it may be useful, and get it tested under conditions of actual use by programmers other than the author. Future versions will be distributed to registered users only. See the file INFORMAL.DOC for details. This document is not intended to teach assembly language programming. It will fully explain the operation of the SVASM02 assembler, and with numerous examples, will guide the user to efficient and successful assembly of 6502 and 65C02 code. RUNNING THE SVASM02 ASSEMBLER SVASM02 is invoked in the usual manner - merely type the program name. The screen will clear and a sign-on line will appear, followed by a prompt for the input file name. It looks like this: SVENSON ELECTRONICS 6502/65C02 ASSEMBLER - V.1.0 - MAY, 1988 Source filename [.ASM]: At this point, enter the requested filename. A valid disk designator may preceed the filename, but a path designation may not. SVASM02 does not support directory paths. If no drive specifier is used, the default logged drive is assumed. Note in the example above the "[.ASM]" following the filename prompt. This is the default filename extension that will be used in the absence of any input filename extension. For example, the filename SOURCE.ASM may be input as SOURCE or as SOURCE.ASM. If the filename extension is anything other than .ASM, it must be specified. Any error situation is immediately displayed, with a repeat of the prompt. The source file is expected to be standard ASCII text, which may be prepared with any suitable editor or word processor. The next prompt is for the object filename: Object filename [.HEX]: Again, disk designations are supported, paths are not, and the default filename extension is .HEX. If no drive specifier is used, the default drive is assumed. A filename must be entered to obtain an object file. If no object file is desired, merely strike the ENTER key. Output is normally to disk as ASCII characters in the standard Intel format (see Appendix B for a description of the HEX file format). Reserved Device Names may be used for directing HEX output to the COM ports, console, or printers. This is done by DOS, and is not supported by SVASM02. Obviously, you do this at your own peril. The results may not be as expected. The final prompt is for the name of the listing or print filename: Print filename [.LST]: The same rules apply here as for the .HEX file, except the listing file may be directed to the screen by entering CON or to the printer by entering LPT. Entering a valid optional drive and filename will cause the print file to be written to disk. If no drive specifier is used, the default logged drive is assumed. Use of the system Reserved Device Names may produce unexpected results, except for CON. Drivers have been included to produce the correct results using CON, and using LPT instead of any of the system names produces a correct printer output. See Appendix A for a description of the LST output file format. Assembly now begins. If any assembly errors are found, the offending numbered line is output to the screen, followed by a line containing the error number and a description of the error. Error output to the screen is automatic, regardless of the presence or absence of a .LST or .HEX file. If a .LST file is being written, the same error sequence will appear in it. Errors are fully discussed anon. Completion of assembly is signaled by the appearance of an ending statement containing the number of bytes assembled and the number of errors, followed by the DOS prompt. INPUT FILE LINE STRUCTURE SVASM02 uses the standard format for assembler input. Each instruction is on a single line, and each line is composed of four fields. A line may start in any column. The fields are: Label Instruction Argument ;Comment All fields are generally optional. The argument field may or may not be required depending on the nature of the instruction. Fields are separated by one or more space or tab characters. The argument field may be separated from the comment field by the comment delimiting semicolon character ";". Label Field Labels are used as references within the code. Their use is optional, but if a label is used it is the first non-blank field on the line. They may be up to six characters long and must begin with a letter. Only the upper case alphabetic characters from A to Z and the numerals 0 to 9 may be used in a label. A label does NOT require a colon. In fact, use of a colon following a label will generate an error. A label may be the only field on a line. Instruction Field The instruction field is composed of microprocessor instructions. All instructions are three upper case characters long. The instruction mnemonic is as described by the manufacturer. The instruction field is the first non- blank field on the line if a label is not used, or if the statement is not an equate or directive. If a label is used, one or more blank or tab characters must separate the label field from the instruction field. For a complete listing of all of the 6502 and 65C02 instructions, see the file TEST02.ASM. Argument Field The argument field contains any argument required by the instruction. It may be a constant, a symbol, register name, or an expression. Numeric constants may be expressed in decimal, octal, hexadecimal, or binary. Quoted string constants are also allowed. See the Arithmetic section for a complete description of constants, symbols, and expressions. Comment Field The comment field is the last field on a line, and must begin with a semicolon (;). Anything, regardless of case, that follows a semicolon is considered commentary information and is ignored by SVASM02. Comments appear in the source listing exactly as they appear in the source line. A blank line is considered a comment, and need not be preceeded by a semicolon. ARITHMETIC Symbols A symbol is a name assigned to represent a value. A symbol, once defined, may not be redefined. Labels are symbols, since the value of the label is the value of the program counter when the label is defined. A label is defined when it appears as the first field on a line. Program Counter The program counter is represented symbolically by the asterisk (*). If the program counter is not defined, a starting value of zero is assumed. The value assigned to the program counter may not be a forward reference. Consider the following sequence: * = $100 ; The program counter is defined a value of 100 hex. FLAG * = * + 1 ; The value of FLAG is 100 hex, and the program counter ; is advanced by 1. START LDA #1 ; The value of START is 101 hex In the above sequence, FLAG is uninitialized storage at location 100 hex. START is a label having a value of the program counter, or 101 hex. Symbols follow the same rules of syntax as labels - up to six characters (A-Z, 0-9), beginning with a letter. Constants A constant is an unsigned numerical value between 0 and 65,535 (decimal). It may be expressed in any of four radices - decimal, hexadecimal, octal, and binary - or may be a quoted string one or two characters long. A decimal constant may contain the numerals 0 through 9, and must have no leading or trailing radix specifier. A hexadecimal constant may contain the numerals 0 through 9 and the upper case letters A through F. It must be either preceeded by the dollar sign ($) character or contain the letter H as the last character. If the trailing H specifier is used, the first character must be a numeral between 0 and 9. An octal constant may contain the numerals 0 through 7, and must be either preceeded by the @ character or trailed by the letter Q. A binary constant consists of up to sixteen 0 and 1 characters, preceeded by the % character or trailed by the letter B. A quoted string constant is any one or two characters enclosed between single quote characters. The value of a single character quoted string is the 8-bit ASCII code value of the character. A two character quoted string has similar characteristics, being the 16-bit value of the characters, in ascending order (from left to right). Note that the double quote is invalid as a string delimiter, and is considered to be a character just like K, a, &, etc. (See the discussion of the .BYTE directive for additional use of the quoted string.) Some examples: 1233 Decimal, no radix specifier $4ACF Hexadecimal, leading radix specifier 4ACFH Hexadecimal, trailing specifier @377 Octal, leading specifier 377Q Octal, trailing specifier %10110 Binary 10100110B Binary 'A' Single character quoted string 'CQ' Two character quoted string Expressions An expression is a symbol, constant, or combination of symbols and constants connected by arithmetic and/or logical operators such that the value of the expression does not exceed 16 bits, or 65,535. The arithmetic operators are: + Addition - Subtraction * Multiplication / Division < Extraction of low 8 bits > Extraction of high 8 bits Arithmetic Operators The four arithmetic operators (+, -, *, and /) apply to addition, subtraction, multiplication, and division, respectively, and warrant no further explanation. The byte extraction operators extract either the low 8 bits or high 8 bits from a 16-bit argument. This is best illustrated by examples: LOW8 = <$1234 ; The value of LOW8 is $34 HIGH8 = >$1234 ; The value of HIGH8 is $12 The logical operators are: AND Logical AND of the arguments OR Logical OR NOT Complement of the argument XOR Exclusive OR of the arguments MOD Remainder SHL n Shift left n bits SHR n Shift right n bits Logical Operators All logical operations assume 16-bit arguments. Leading bits not contributing to the value of the operation are either 0 or 1, as appropriate. For example, NOT 0 has a value of $FFFF, while $1234 AND $34 has a value of $0034. Results of a shift operation (SHL n or SHR n) do not wrap around, ie., a bit shifted right out of bit 0 or shifted left out of bit 15 is lost. Evaluation of expressions is from left to right only. There is no hierarchy, and parenthesis are not allowed. Examples of all of the above may be had by assembling the TEST02.ASM file. ADDRESSING MODE SYNTAX The generation of the appropriate opcode by SVASM02 is totally dependent on the addressing mode used. The syntax of the instruction and its argument (if any) determines the addressing mode, and therefore what opcode will be generated. The 6502 uses thirteen addressing modes, and the 65C02 uses all of these with two additional. The following descriptions of each addressing mode give an example illustrating the syntax of each: 6502 Addressing Modes: Zero Page - LDA $20 Only the low eight bits are specified and refer to an address of $00FF or less. The high eight bits of the address are assumed to be 0. This is a very efficient addressing mode for the 6502/65C02. Absolute - LDA $125F The second and third bytes of the instruction contain a 16-bit address. Any address within the 6502 64K address space may be specified. Immediate - LDA #$FF The second byte of the instruction contains immediate data requiring no further addressing. The # symbol signifies immediate data. The value of the data is limited to 8 bits. Indexed Zero Page - LDA $20,X or LDA $20,Y The second byte of the instruction contains the value of a base address on page zero to which is added the contents of the X or Y register. The result is the effective page zero address and must not exceed 255 (decimal). Indexed Absolute - LDA $453D,X or LDA $453D,Y The second and third bytes of the instruction contain the value of a base address to which is added the contents of the X or Y register. The result is a 16-bit value which is the effective address. The value must not exceed 65,535 (decimal). Zero Page Indexed Indirect - LDA ($20,X) The second byte of the instruction is added to the contents of the X register, with any carry discarded. The result points to a location on page zero which contains the low eight bits of the effective address. The next higher page zero address contains the high eight bits of the effective address. CAUTION - Both memory locations containing the effective address must be on page zero. SVASM02 has no way of checking this at assembly time, so the programmer is cautioned to heed this warning. Indirect Indexed - LDA ($20),Y The second byte of the instruction points to a page zero location. The contents of this location is added to the contents of the Y register, producing a result which is the low 8 bits of the effective address. Any carry resulting from the addition is added to the contents of the next page zero address, the result being the high 8 bits of the effective address. See the CAUTION in the preceeding paragraph. Absolute Indirect - JMP ($122F) The second and third bytes of the instruction contain a 16-bit address. The contents of that address contain the low 8 bits of the effective address, and the next higher memory location contains the high 8 bits of the effective address. This addressing mode applies only to the JMP instruction. Implied - TSX The addressing is implied by the instruction, and no further address is required. Acumulator - LSR A This addressing mode is but a single byte, which specifies an operation to be performed on the accumulator. The argument must be the single letter A. Relative - BEQ *+5 The second byte of the instruction contains an 8-bit offset which is added to the program counter value of the next instruction. The result is the new value of the program counter. The assembler uses the present value of the program counter to make the calculation. When writing the code, use the value of the program counter at the beginning of the present line. The assembler takes this into account when computing the offset, and the proper offset to the target is produced. This avoids undetected errors in the offset. For example, . . 12 1000 F003 BEQ *+5 13 1002 200041 JSR FIX3 ; A subroutine at $4100 14 1005 4C0010 TARGET JMP $1000 . . Line 12 (program counter = address 1000) specifies a branch to the target at 5 bytes beyond the present program counter to address 1005. The assembled offset is 03, which is the target relative to the program counter at line 13. This 2 byte difference is due to the way in which the 6502/65C02 handles the program counter and relative addressing. The permissible range of the offset is -128 to +127 bytes relative to the next instruction, or -126 to +129 relative to the present instruction. 65C02 Additional Addressing Modes: Zero Page Indirect - LDA ($20) The second byte of the instruction contains a page zero address whose contents is the low 8 bits of the effective address. The high 8 bits of the effective address is in the next highest page zero location. See the CAUTION under Zero Page Indexed Indirect above. Indexed Absolute Indirect - JMP ($203B,X) The second and third bytes of the insruction contain a base address. The contents of the X register is added to it, and the result points to a memory location containing the low 8 bits of the effective address. The high 8 bits are loaded from the next highest memory location. In the above examples numeric constants were used as arguments to illustrate the magnitude of the argument (8 or 16 bits). In actual use, the argument may be expressed symbolically as well. Symbolic zero page (8 bit) arguments must be defined prior to their use in an expression. While it would be correct to use a 16 bit value with the high 8 bits set to zero, to do so is not good programming practice and is not allowed by SVASM02. For example: STA TEMP2 ; TEMP2 = $12 This will generate a "Forward Reference to Page Zero" error. If the order was reversed, TEMP2 = $12 ; STA TEMP2 no error would be generated. There are instructions where this does not apply, however. Those instructions that have no zero page mode may use an absolute argument with a value anywhere in the range of 0 to 65,535. ASSEMBLER DIRECTIVES (Pseudo-ops) SVASM02 utilizes several directives, or pseudo-operators, for directing the assembly. These include directives for page length and width control, printer control, listing control, conditional assembly, CMOS (65C02) assembly, inclusion of source code from an alternate file, and definition of byte and word storage. All pseudo-ops must begin with a period. The pseudo-ops are as follows: .BYTE ; Defines initialized byte storage .WORD ; Defines initialized word (two bytes in low/high format) .CMOS : Allows assembly of 65C02 instructions .END ; Defines the physical end of the source code .LIST ; Turns on listing if it had been off .NOLIST ; Turns off assembler listing .INCLUDE ; Reads source code from an alternate disk file .PAGE ; Controls page length .WIDTH ; Controls page width .PRINTC ; Outputs printer control characters .IF ; Assembles following statements if argument is non-zero .ELSE ; Alternate assembly if .IF argument is zero .ENDIF ; Terminates conditional assembly .LISTF ; List but do not assemble false conditionals A detailed description of each pseudo-op follows. .BYTE The .BYTE pseudo-op is perhaps the most used. It initializes storage of its arguments in the code at the address of the value of the program counter at the beginning of the line. The arguments may be constants, symbols, expressions, or quoted strings. Each individual argument must be separated from the next by a comma. The magnitude of each evaluated argument must not exceed 8 bits. In the case of quoted string arguments, the only limit is the length of the line. The delimiter for the quoted string is the single quote character. A double quote has no meaning in SVASM02 other than as a character. To include a single quote character as part of the quoted string, use two single quotes together. Examples: .BYTE $45,$77,$FF,0,3 ; Constants .BYTE SHELL + 4 ; Expression (value of 8 bits or less) .BYTE 'This Can''t be' ; Quoted string with embedded ; single quote .WORD Similar to .BYTE, the .WORD pseudo-op assembles 16-bit values at the address of the value of the program counter at the beginning of the line. Since the 6502/65C02 handles 16-bit values (addresses) in low byte/high byte order, the .WORD directive assembles the 16-bit values of its arguments in low/high order. The arguments to .WORD follow the same rules as for .BYTE, except the value of each argument may be within the range of 0 to 65,535. Examples: .WORD START ; The 16-bit value of START is placed in the code .WORD ASSEM+9 ; 9 is added to the value of ASSEM, and the result ; is placed in the code .CMOS Directs SVASM02 to assemble 65C02 instructions in addition to 6502. The default is off (do not assemble 65C02). If assembly of 65C02 instructions or address modes is attempted without first invoking .CMOS, an error will be generated. The .CMOS directive has no arguments. .END This directive causes assembly to stop, and must be used as the last statement in the source code. No further assembly occurs following the .END directive. The .END directive has no arguments, and its omission causes an error. .END must be used in .INCLUDE files as well. The .END in an .INCLUDE file causes termination of assembly of the .INCLUDED source statements and a return to the primary source file. .LIST This directive, together with its complementary .NOLIST, may be used to selectively list the assembled source code in the output file. If no LST file or device is selected at program invocation, the .LIST directive is ignored. The default is on (list assembler output). There are no arguments. .NOLIST Turns off assembler output listing. Source code lines following the .NOLIST are counted and assembled, but generate no LST output. If no LST file or device is selected at program invocation, the .NOLIST directive is ignored. The default is .LIST, and there are no arguments. .INCLUDE This directive causes SVASM02 to read source code input from the file named as the argument. The filename must be valid, and may include a disk drive specifier. Omission of a drive specifier causes the default drive to be used. A pathname may not be used. The source code in the INCLUDEd file must contain the .END directive. Its omission will cause an error. INCLUDEs may not be nested (only a single open INCLUDE at a time is allowed). Example: .INCLUDE DISTRIB.TAB ; Source code is taken from the file named ; DISTRIB.TAB on the default logged disk. .PAGE This directive controls the length of the LST output page and causes a header to be printed on the top of each new page. The header includes the assembler name and version number, the name of the file being assembled, the date and time at which assembly was started, and the page number. Four blank lines separate the header from the output. The default is no paging. The .PAGE directive may or may not have an argument. If no argument is specified, paging is initiated at the default 58 output lines per page or at the previous number of lines per page if a previous .PAGE n had been used. If a .PAGE 0 is specified, paging is turned off if it had been on. .PAGE n will initiate paging at n lines per page. The maximum lines per page is 255. A PAGE may be used to cause a page eject. The .PAGE directive is not printed, and has no line number assigned. Examples: .PAGE ; Initiate paging at 58 lines/page or the previous value .PAGE 60 ; Use 60 lines/page .PAGE 0 ; Turn off paging .WIDTH This directive controls the number of character spaces on the LST output line. The default is 76, and includes the neccessary fill spaces for tab characters. A tab character is assumed to be eight character spaces long, and occur every eight character positions. Beginning at position 1, a tab can position the print head at column 9, 17, 25, 33, etc. If a tab character is encountered between the tab settings, blanks are added to position the print head at the next tab stop. The .WIDTH directive must have an argument, and its value must be in the range of 64 to 255. Any input source code characters beyond the number specified in the argument are assembled, but are ignored in the LST output. .PRINTC Many printers use "escape codes" or other control characters to control pitch, form length, page width, etc. The .PRINTC directive is intended to send initializing or control characters to the printer. The argument contains a string that is evaluated as binary bytes by SVASM02 and is written to the LST output device prior to any other output. The bytes are not counted against line width, the line is not counted and it does not appear in the LST output. There is no default. When used, the .PRINTC directive should be the very first statement in the source code. Example: .PRINTC '[x2,' ; Causes the four byte string [x2, to be sent ; to the LST output file or device. .IF, .ELSE, .ENDIF, .LISTF These pseudo-ops will be discussed together, since they are the so-called conditional assembly directives. A conditional assembly sequence consists of the openning .IF statement with its argument, source statements, and the closing .ENDIF statement. If the argument of the .IF evaluates non-zero (true), the source statements between the .IF and .ENDIF are assembled. If the argument evaluates zero (false), the statements between the .IF and .ENDIF are not assembled. Statements within a false conditional are not listed on the LST output unless .LISTF (list false conditionals) has been invoked. The .ELSE directive is used between the .IF and .ENDIF to permit alternate assembly or non-assembly of the code following, depending on the value of the IF argument. This is best shown by illustration: .IF arg . If arg is non-zero, the statements up to the . .ELSE are assembled and those between the .ELSE . and the .ENDIF are not. . .ELSE . If arg is zero, the statements between the .ELSE . and the .ENDIF are assembled and those between the . .IF and .ELSE are not. . .ENDIF The argument to the .IF is required, and may be any constant, symbol, or expression. .ELSE, .ENDIF, and .LISTF do not require arguments. There are no defaults to conditional assembly. Conditionals may be nested up to 16 levels. It should be noted that this version of SVASM02 does not allow the use of relational operators such as EQ, LT, GT, etc. in the argument to the .IF. ERRORS Fatal Errors There are three fatal errors possible in SVASM02. Each causes the program to stop and an error message to be displayed on the screen. Control is returned to DOS. 1. Directory full - An attempt was made to create a file entry in a disk directory that contained no available slots. Reduce the number of files on the disk or use another disk. 2. Input file read error - The source file is corrupted or otherwise not readable. Try another copy of the file. 3. Disk full - An attempt was made to write data on a full disk. Use another disk or delete files to make room. Invocation errors These errors are non-fatal, merely causing a reissuing of the prompt. 1. Filename error - An incorrect syntax was used to specify a filename for the source, object, or list file. 2. Invalid drive - The disk drive specified does not exist or is not avaialable. 3. File not found - The source file could not be found on the drive specified. Assembler Errors There are 25 possible assembly time errors. Each is numbered, and when encountered, is output to the screen along with the line containing the error. For example, 381 2079 .PSGE 60 ; Use 60 lines/page *** 10 *** Unidentified directive The first line is the assembler output of the line containing the error. In the above example, 381 is the line number and 2079 is the program counter value. The remainder of the line is as input. The error message number appears before the description of the error and is the reference to the detailed discussion of the error in this document. If an output file is being generated or there is output to a list device, the same error sequence appears there. Regardless of the output medium, all errors are output to the screen as shown above. For errors occurring in lines containing instructions, one, two, or three NOP's ($EA) are assembled depending on the number of bytes expected to be required for the instruction. 1 Undefined symbol - A reference was made to a symbol that has never been defined. This could be caused by a misspelling of a valid symbol or label name, or omission of a line of code. An improper numeric argument or directive name could also be considered a "symbol" and as such, could cause this error. 2 Label or symbol previously defined - An attempt was made to redefine a symbol or use a label more than once. Once defined, SVASM02 does not allow a symbol to be redefined. 3 Syntax error - The stucture of the line is not recognized. Check the statement for proper syntax, missing arguments, etc. 4 Illegal first character in label or symbol - Labels and symbols must begin with a letter. Am improperly structured or used numeric argument may also cause this error. 5 Forward reference to page zero - All references to addresses on page zero must be known before they are used. See the discussion on page 6 under Addressing Modes. 6 Label or symbol more than 6 characters - The present version of SVASM02 limits the number of characters in a label or symbol to six. 7 No .END directive in INCLUDE file - The .END directive is required to terminate assembly. An end of file was reached without finding the .END directive. 8 Forward reference in equate or origin - An expression contained a symbol which was not defined prior to its use to define the program counter or an equate. 9 (Reserved) 10 Unidentified directive - A directive or pseudo-op was found that is not in the list of valid directives. Check for a stray leading period or bad spelling. 11 Invalid quoted string - An attempt was made to use a quoted string constant greater than two characters long, or there was a missing quote character. 12 Branch target out of range - The target address of a branch instruction was beyond the maximum allowed displacement from the source instruction. See the discussion on relative addressing. 13 Invalid addressing mode - An attempt was made to use an addressing mode that is invalid for the instruction. See the file TEST02.ASM for a complete listing of all valid addressing modes for all instructions. 14 Invalid numeric argument - A numeric argument contained a character invalid for the radix used. 15 Arithmetic overflow - The result of an arithmetic operation exceeded 65,535 (decimal). 16 No .END directive - The last statement in the source file was not an .END directive. .END must be encountered before the physical end of the file. 17 Expression value > 8 bits - An arithmetic operation produced a result greater than 255 (decimal) for an instruction or addressing mode requiring a single byte value. 18 Division by zero - The divisor in a division operation had a value of zero when the operation was attempted. 19 CMOS assembly not selected - An attempt was made to use a 65C02 instruction or addressing mode before invoking the .CMOS directive. 20 Open .IF limit exceeded - The number of open conditional assembly (.IF directive) exceeds the maximum of 16. 21 Forward reference in conditional - The value of the argument in an .IF directive was unknown at the time the .IF was encountered during the first pass. The argument value must be known before the .IF can be openned. 22 No open .IF - An .ELSE or .ENDIF was encountered for which there was no corresponding .IF directive previously specified. 23 .INCLUDE file already open - An attempt was made to .INCLUDE a file that has already been openned (.INCLUDEd). 24 INCLUDE filename error - A syntax error has occurred in the filename given in an .INCLUDE directive. 25 Invalid drive name - The disk drive specifier in a filename to be .INCLUDEd is invalid. 26 INCLUDE file not found - The file specified in an .INCLUDE directive cannot be found on the specified disk drive or currently logged disk if no disk specifier is used. APPENDIX A SVASM02 LST Output File Description The output fragments which follow were extracted from the TEST02.LST file to illustrate the format of the assembler output. In general, the first 33 spaces on a line are generated by SVASM02. The remainder of the line is a copy of the input code. . . 18 = 0047 QUOTE1='G' ;SINGLE QUOTE . . Line 18 contains an equate. The line number appears in the first four spaces on the left. The = signifies a valid equate, having the hexadecimal value of 0047. The several spaces between the value and QUOTE1 are the remaining spaces up to column 32, followed by tab expansion spaces up to the QUOTE1. The spaces between the 'G' and the ; are tab fill spaces such that the comment delimiter (;) starts in a column which is a multiple of 8, plus 1. The input source code contained tabs in these spaces. . 52 ; 53 ; BYTE AND WORD DIRECTIVES 54 ; 55 1006 0D0A5356 .BYTE $0D,$0A,'SVENSON ELECTRONICS','$' 100A 454E534F 100E 4E20454C 1012 45435452 . Lines 52 through 55 are the output from commentary information and a .BYTE directive. The ; in lines 52-54 are in column 33, having been in column 1 in the input file. The byte output begins in line 55. The 1006 is the hexadecimal address (program counter) at which the bytes were assembled. The eight hexadecimal characters which follow represent the value of the first four bytes of the data assembled. The remainder of the line is as input. The three unumbered lines following are the remaining output for the directive. For .BYTE and .WORD directives, the line number is not incremented if additional lines are required to complete the output of the data. Line numbering resumes at the next statement. . 65 1024 AD0230 LDA PORT1 66 1027 29FF AND #$FF 67 1029 8D0530 STA DAT1 . Lines 65-67 are typical instruction code output. Note that addresses are listed in lowbyte/high byte order exactly the way they appear in memory. . 86 102F EAEA BRA *-126 *** 19 *** CMOS Assembly not selected . Line 86 contains an error, with the error message on the following line. Since the branch instruction is expected to generate two bytes of machine code, two NOP's (EA) are inserted in place of the code that would be generated had there been no error. In the error message line, the 19 refers to the error number, a discussion of which may be found in the main documentation under ERRORS. . END OF SVENSON ELECTRONICS 6502/65C02 ASSEMBLER - VERSION 1.0 BYTES ASSEMBLED: 510 NO. OF ERRORS: 46 SYMBOL TABLE: LINE SYMBOL VALUE DEFINED CROSS REFERENCES BIAS 0007 48 BVAL1 009D 34 47 BVAL2 009D 35 51 CHECKP 2091 381 The above output fragment appears at the end of the code output. The number of bytes asembled is given, and represents the actual count of bytes assembled. Gaps in the address space of the program, such as for uninitialized storage, are not counted. The number of errors is also stated. The alphabetically sorted symbol table follows, with appropriate column headings for the symbol name, its hexadecimal value, the decimal line number in which it was defined, and decimal listing of cross-reference line numbers. The above example shows only a single reference for two symbols, but multiple references are listed on the same line up to the maximum number of spaces allowed by the WIDTH directive. Any additional references are listed on the following lines. APPENDIX B SVASM02 Object File Format The object file consists of records of ASCII hexadecimal characters in the Intel format. A typical record looks like this: :101006000D0A5356454E534F4E20454C45435452B8 Byte 0 A colon character, signifying the beginning of the record Bytes 1-2 Hexadecimal value indicating the number of loadable bytes in the record. The maximum is 10 (16 decimal). Bytes 3-6 Hexadecimal address where first byte of the record will be loaded. Bytes 7-9 Always 00. Bytes 10-on Hexadecimal characters representing the actual data bytes. Last two A checksum. The checksum is the two's complement of the 8-bit bytes sum of the value of all bytes (not the ASCII) with carry discarded. It includes the byte count, load address bytes, and loadable data bytes. The last record contains values of zero for byte count, load address, and checksum. It effectively is :0000000000.